Extractor Exhaust - what does that mean

[Tidybuoy]

Can sombody explain what they mean by "extractor" exhaust?

I understand that the pipes are twisted around to match up #1 & 3 & #4 & 2 cylinders but what does that all mean & why is that better than stock. Why didn't the factory do it that way?

I had an extractor setup on a VW bug, many years ago & it seemed to add power but that could have just been in my head after noticing the improved sound.

My assumption has been that the Bursch setup reduces back pressure & that is why there "may" be inproved power but if anyone has more info - I'd really appreciate it...............Vern

[Dave at Pelican Parts]

The complete explanation is long an fairly ugly...

The short version is that the exhaust gases travel in pulses (the valve opens, the contents of the cylinder get pushed out, the valve closes). "Behind" each pulse is a little vacuum. If you merge the exhaust pipes together the right way, you can actually use those little vacuums to suck out more of the exhaust gases from the next exhaust valve to open up. This more effectively scavenges all the burned, used-up air out, and creates a slightly lower-pressure area in the cylinder which helps pack in a tiny bit more air the next time the intake valve opens.

There are actually about three or four effects that go on, but the net product is that they are used to scavenge more of the exhaust gases out.

Not precisely less back-pressure, but I guess that idea will do as a first approximation.

--DD

[Tidybuoy]

Good Answer! Thanks!

[Zeke]

Does the same thing an expansion chamber does on a 2-cycle motorcycle or kart engine. Dave's explanation is good. There is a bit more. Even head pipes that are not merged have a effect on the performance. Too short or beyond the optimum length and performance will suffer. So, if the exhaust has to go any further, it is "collected" in a larger secondary pipe and run to an exit point. So, these "pulses" are staged in the primary pipe and them again in a secondary pipe to keep the gases from building uneven and out of time pressure which unbalances the system. That can lead to some cylinders to run lean and others to run a little richer. The design of exhaust systems for the real environment, i.e., within the body work of a Formula 1 car, is high art. That, as opposed to the 8 big single pipes on a fuuny car. Even those have a "tuned" length.

[pbanders]

Also remember that the extraction effect (in most designs) is at a maximum only in a narrow RPM band.

Design of a well-engineered motor with a wide torque band and high peak power requires integrated design of all systems - intake, exhaust, valve timing and lift, combustion chamber, ignition, and fuel delivery. Changing one thing in the system can sometimes have unanticipated effects on the entire system.

[jnp914]

I got the newest issue of Car Craft yesterday in the mail. There is an excellent discussion on headers, tube length, diameter, collectors, etc that addresses almost all that has been touched on here.